1. Fields of the Invention
The present invention relates to an arrangement for determining the direction of the energy center of a luminous object, comprising a lens forming an image of said luminous object on a photo-sensitive detector.
2. Art Background
A particularly advantageous use of the invention is in the field of observing luminous objects, such as the sun for example, more specifically for positioning ground-based radar or for supervising the behavior of missiles in their orbit.
Among the arrangements for determining the direction of the energy center of a luminous object defined in the opening paragraph, solar view finders, using a unidimensional charge-transfer strip as a photo-sensitive detector, are known. This type of field finder, however, has the disadvantage of supplying only a single piece of information, regarding the direction of the luminous object aimed at, that is to say the position of the gravity center of the spot image on the axis of the strip.
In order to obtain the two information components, needed for a complete determination of the direction of the energy center of the luminous object, recourse may be had to a photo-sensitive detector, constituted by a charge-transfer matrix. These arrangements, for example of the type marketed by the firm of Thomson-CSF under the type designation TH 7863, look like a mosaic of image elements divided into two parts: a first half, the photo-sensitive zone, is intended to receive and detect the light radiation coming from the object aimed at, and the second half, covered with an opaque film, serves as a memory in which the information components received by the first half of the matrix are stored by means of charge transfer. This reduction of the surface of the photo-sensitive detector by a factor 2 has for its consequence that the field of vision is limited, which is particularly disadvantageous when one wants to realize an arrangement by means of which the direction of a luminous object can be obtained in an autonomous manner, i.e. without the assistance of auxiliary equipment, which would first move the view finder roughly in the direction of the object searched. To that end, it is advisable to have available the widest field of view offered by the total surface area of the charge transfer matrix, while using an identical detector, but whose memory zone, which is not covered by an opaque film, may then also be used as the photo-sensitive zone. However, the use of such a matrix without a memory is not to be expected because of the inevitable appearance of a vertical luminous streak which is superimposed on the useful image and which more specifically reduces the contrast as a consequence thereof.
In fact, at the end of a period known as the integration period, which is determined such that the spot image reaches a sufficient energy level, the matrix is read by transferring the successive lines to an output register integrated into said matrix. A new image of the luminous object is formed on the photo-sensitive zone during each read cycle of the output register, as the transfer of lines and their reading into the output register are not instantaneous and in that the matrix is permanently exposed to light. The total number of these images obtained between two integrations constitute said annoying luminous streak, whose equivalent integration period is equal to the read time of the spot image. In general, the read time of the spot image cannot be neglected relative to the integration period, especially the luminous object aimed at being very bright, for example the sun, when the integration time is comparatively short. It follows that the luminous streak is sufficiently large to limit the contrast in an unacceptable manner.